γ-aminobutyric acid, chemical name 4-aminobutyric acid, is also known as aminobutyric acid or piperidinic acid. Its molecular formula is C4H9NO2, and its molecular mass is 103.1. It appears as a white or off-white crystalline powder; it is a hydrophilic amino acid and is very soluble in water. Its structural formula is as follows:

γ-Aminobutyric acid is a naturally occurring, non-proteinogenic amino acid that is widely distributed in prokaryotic and eukaryotic organisms. In mammals, γ-aminobutyric acid is an inhibitory neurotransmitter that mediates more than 40% of inhibitory nerve signals. It has important physiological functions and broad application prospects in medicine and food industry.
In medical research and applications, γ-aminobutyric acid has efficacies in, such as, blood pressure-lowering, anticonvulsant, seizure prevention, sleep quality improvement, anti-depression, and brain-cell improvement. The latest researches show that γ-aminobutyric acid also has further efficacies in skin-aging prevention, body odor elimination, lipid metabolism improvement, atherosclerosis prevention, and weight loss. In the food industry, γ-aminobutyric acid can be used in the production of food additives, development of functional dairy products and bakery products. It can also be employed in sports food and beverage industry. On Sep. 27, 2009, the Ministry of Health of the People's Republic of China approved γ-aminobutyric acid as a new resource food.
Patents CN101928736A, CN103509831A, CN104531795A proposed the preparation of γ-aminobutyric acid via evaporative concentration and solventing-out crystallization with 95% ethanol. Patent CN102242161A proposed the preparation of γ-aminobutyric acid by evaporative concentration and cooling crystallization. These different methods all yield γ-aminobutyric acid anhydrate as the product. The crystal morphology of the product is needle-shaped or sheet-shaped, its main particle size is small and unevenly distributed, its bulk density is low and its flowability is low. In addition, anhydrous γ-aminobutyl is highly hygroscopic; when exposed to air, it easily absorbs water and agglomerates into clumps, which is not suitable for further processing and use.
Therefore, it is necessary to provide a γ-aminobutyric acid hemihydrate crystal which is stable, does not easily absorb moisture and agglomerate, has a large main particle size, uniform particle size distribution, high bulk density and good flowability, and a preparation method thereof.